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Rising seas in India and the world: freshly assessed threat

The number of people in India threatened by rising sea-levels is at least seven times more than previously estimated, a new research has revealed. The research, published in Nature Communications, has found large areas on the eastern as well as western coastlines under threat of rising sea levels, including Mumbai on the west and Kolkata on the east.

It says 36 million people along the Indian coastlines currently live on land that will fall below the annual flood level by 2050, exposing them to risks of flooding, damage to infrastructure, loss of livelihood, or permanent displacement. The previous estimate was of five million people in these areas being exposed to these risks.

How the study was done

Researchers Scott Kulp and Benjamin Strauss of Climate Central, an independent organisation of climate scientists, have reported that they have developed a new tool that measures elevation of land from mean sea levels with much greater accuracy than earlier models. Their study claims that previous methods to measure land elevation suffered from large errors in most of the world apart from the US, Australia and parts of Europe. Land elevation data in most of these other areas came from satellite measurements done by a NASA project called Shuttle Radar Topography Mission, or SRTM.

The study says the error in the measurements came from the fact that often the tops of trees or buildings were taken to be the protrusions of earth. Thus, SRTM measurements even in the coastal cities of the US often overestimated land elevations by as much as 15.5 feet on an average. Their new tool, called CoastalDEM (or Coastal Digital Elevation Model), which uses artificial intelligence and machine learning on 51 million data samples, brought down this error to less than 2.5 inches on an average, it says.

The threat projection

The study claims to remove over-estimations in the assessment of land elevations in coastal areas. As a result, it finds that much larger areas of land were threatened by rising sea levels because of climate change. Consequently, a significantly higher population group was at risk.

A map of Mumbai based on the new study, and prepared by The New York Times, shows a much higher threat projection than earlier. (Source: NYT)

The study found that 300 million people, and not 80 million as estimated earlier, across the globe were currently living in areas that were below the annual coastal flood line. By the turn of this century, land that is now home to 200 million of these people would be permanently below the high tide line.

Almost 80 per cent of these 300 million people live in China, Bangladesh, India, Vietnam, Indonesia and Thailand. China alone accounted for 43 million.

Vulnerable areas in India

The new tool has found that in particular, the western coastline near Bhuj, Jamnagar, Porbandar, Surat, Bharuch and Mumbai are much more susceptible to rising sea levels than earlier assessments. On the eastern side, almost the entire coastline of West Bengal and Odisha have been found under threat. Except for some areas near Kakinada, the threats to the coastlines of the southern states have not been affected by the new measurements.

The study has serious prediction for India for 2050. “By that year, projected sea level rise could push average annual floods above land currently home to some 36 million people. West Bengal and coastal Odisha are projected to be particularly vulnerable, as is the eastern city of Kolkata,” it says.

Source: The Indian Express

Relevant for GS Prelims & Mains Paper III; Environment & Biodiversity

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